1. Field of the Invention
This invention relates to a two-dimensional visual display of light-emitting diodes to create dot-matrix, segmented character, bargraph and/or annunciator visual displays. Such displays are especially suited for the visual display output of aircraft instruments in the cockpit of aircraft.
2. Related Art
Visual aircraft instrument displays have previously included light-emitting diodes (e.g., for annunciator light outputs). However, a prior dot-matrix display for the STRIKEFINDER(copyright) atmospheric electrical discharge detector and display available from Insight Avionics Inc., uses a gas plasma display which has barely adequate brightness and a limited life. Other competitive instruments have used expensive CRT displays to obtain sufficient dot-matrix resolution.
A surface mounted light-emitting diode (LED) is also known and readily available commercially (e.g., from Lumex Corporation) with various different emitted colors of light (e.g., green, yellow, super yellow, red and super red). LED arrays have been made by applying chips to ceramic substrates and using wire bonding connections which are not too practical since microscopic bond wires are fragile and single chips are difficult to replace. However, conventional surface mounting techniques require a minimum sized surface bonding solder pad that extends beyond the edges of the surface mounted component by at least about 0.010 inch. For example, the recommended LED surface mount solder pad layout by Lumex Corporation would have solder pads extending outwardly end-to-end by 0.090 inchxe2x80x94for a surface mounted LED that is only 0.063 inch in total length (thus leaving 0.0135 inch of solder pad extending at each end beyond the LED itself). Such extended bonding solder pad layouts have conventionally been considered necessary so as to provide sufficient liquid solder meniscus to accurately center the surface mounted component at the desired location and/or for other reasons.
Perhaps for such reasons as these, it is not believed that surface mounted LEDs have previously been used to realize relatively dense dot-matrix or segmented character visual displays. SUMMARY OF THE INVENTION
This invention utilizes a discovery that one can use substantially less than 0.010 inch excess solder pad dimensions placed with conventional surface mounting machinery (with appropriate cautionary steps being taken to prevent undesired solder flow through solder pad connection vias) to obtain relatively dense two-dimensional visual display of light-emitting diodes surface mounted on a printed circuit board. Each diode provides a dot of output light when activated and the diodes can be disposed in relatively densely packed two-dimensional row and column arrays.
In some exemplary embodiments, the printed circuit board is substantially planar and each pair of conductive mounting pads is connected through corresponding anode and cathode vias to different respectively corresponding printed conductive circuit anode and cathode row/column connections in different printed circuit board planes (substantially parallel to the printed circuit board on which the diodes are mounted).
If the two-dimensional visual display is to provide a dense dot-matrix display with equal vertical and horizontal spacing of output light dots, then the oblong-dimensioned light-emitting diodes are preferably oriented differently in adjacent rows and columns of the arrays. In particular, a preferred embodiment utilizes a herringbone pattern of rectangularly-shaped light-emitting diodes such that the diodes of one row or column are oriented orthogonally with respect to the diodes in another adjacent row or column. In this embodiment, the rows and columns of light-emitting portions of the diodes are offset with respect to one another in adjacent rows and columns.
In the preferred exemplary embodiments having the most dense packing of light-emitting diodes, it is preferred that the conductive pads extend beyond the end edges of the light-emitting diodes by a distance substantially less than 0.010 inch (i.e., the conventional minimum extension). In particular, in preferred exemplary embodiments, the extension distance of the solder pads is only approximately 0.001 inch. In this arrangement where the diodes have an oblong (e.g., rectangular) shape with a long dimension D, they are arrayed so as to have a spacing P between diode light dot outputs that is substantially less than D in both row and column directions.
In one exemplary embodiment, the two-dimensional visual display as previously discussed is incorporated within an assembly of successively stacked substantially planar elements including an optical lens/graticule layer, a light polarizing filter layer, the light-emitting diode array on its multi-layered printed circuit board having row and column connection points at its periphery, and a driver printed circuit board connected to the peripheral connection points of the diode array through connections disposed within at least one spacer structure and having integrated circuit LED drivers on the driver printed circuit board.
In one exemplary embodiment, the apparatus is associated with a data processor having input sensors for sensing electrical discharges in the atmosphere and outputting signals to the driver printed circuit board so as to produce a plan view on a dot-matrix visual display of detected electrical atmospheric discharges (e.g., lightning strikes). Such a system is available, for instance, from Insight Avionics Inc. marketed under the trademark STRIKEFINDER(copyright).
Preferably the surface mounted LED array is coated directly with an anti-reflective coating (e.g., a xcex/4 thickness so as to reduce ambient light-reflections from aircraft instrument display. Concurrent use of an overlayed circularly polarized sheet is also preferred to further reduce ambient light reflections.
Another embodiment of this invention is preferably utilized as part of a graphic engine monitor (GEM) which provides bargraphs and/or alphanumeric data related to real time aircraft engine conditions (e.g., the cylinder head and/or exhaust gas temperature for each cylinder of a multi-cylinder aircraft engine, the turbine inlet temperature of a turbo charger, etc.). For this exemplary application, a two-dimensional visual display in accordance with the invention is disposed under a multi-apertured mask representing a segmented character display (e.g., including seven-segment apertures corresponding to the conventional seven-segment character displays). Preferably in the exemplary embodiment, each diode is associated with a given segment of the character display and all diodes for one character can be simultaneously activated (e.g., together with a column of LEDs representing a bargraph or the like).
In the exemplary embodiment of a segmented character display in accordance with this invention, each diode has an oblong (e.g., rectangular) shape with the long dimension being oriented at a substantial slant angle with respect to both horizontal and vertical character dimensions. For example, in the exemplary embodiment, the slant angle is substantially 45xc2x0. In this exemplary embodiment, the seven-segment character mask is associated with seven diodes having such oblong shape and arrayed vertically (at the substantial slant angle) in stacked linear groups of two, three and two. If desired, a further diode can be included with the middle linear slanted group of three diodes and associated with a decimal point aperture in the mask located at the lower left portion of the character.
The two dimensional visual display of this invention may also utilize adjacent light-emitting diodes having different colors of emitted light which are connected for selective activation so as to provide different colors of light output for a given display element (e.g., a bargraph). The adjacent differently colored light outputs may also be co-activated so as to provide light output as a mixture of colors from plural light-emitting diodes.